We address the challenge of reconstructing the energy of three ultrahigh-energy cosmic rays registered with a small fluorescence telescope EUSO-TA that operated in 2015 at the site of the Telescope Array experiment in Utah, United States. Each of these events was recorded within one time frame. Conventional methods of energy reconstruction are not applicable in this case because the events do not have light curves but a single data point. As an alternative, we consider a number of approaches based on artificial neural networks. We demonstrate that a signal recorded by a fluorescence telescope within one time frame might be enough to reconstruct the energy of a primary particle with reasonable accuracy using an ensemble of simple convolutional neural networks. Contrary to the conventional approach, reconstruction of the shower geometry is not needed for this. More than this, preliminary estimates can be obtained even without recognizing the shower track. However, there remain some problems that do not allow us to claim that the suggested method is universal and always works. We discuss difficulties that we faced and possible ways of improving the method.

Mini-EUSO is a wide Field-of-View (FoV, 44$^{\circ}$) telescope currently in operation from a nadia-facing UV-transparent window in the Russian Zvezda module on the International Space Station (ISS). It is the first detector of the JEM-EUSO program deployed on the ISS, launched in August 2019. The main goal of Mini-EUSO is to measure the UV emissions from the ground and atmosphere, using an orbital platform. Mini-EUSO is mainly sensitive in the 290-430 nm bandwidth. Light is focused by a system of two Fresnel lenses of 25 cm diameter each on the Photo- Detector-Module (PDM), which consists of an array of 36 Multi-Anode Photomultiplier Tubes (MAPMTs), for a total of 2304 pixels working in photon counting mode, in three different time resolutions of 2.5 ${\mu}$s, 320 ${\mu}$s, 40.96 ms operation in parallel. In the longest time scale, the data is continuously acquired to monitor the UV emission of the Earth. It is best suited for the observation of ground sources and therefore has been used for the observational campaigns of the Mini-EUSO. In this contribution, we present the assembled UV flasher, the operation of the field campaign and the analysis of the obtained data. The result is compared with the overall efficiency computed from the expectations which takes into account the atmospheric attenuation and the parameterization of different effects such as the optics efficiency, the MAPMT detection efficiency, BG3 filter transmittance and the transparency of the ISS window.

Context. Observations of meteors in the Earth's atmosphere offer a unique tool for determining the flux of meteoroids that are too small to be detected by direct telescopic observations. Although these objects are routinely observed from ground-based facilities, such as meteor and fireball networks, space-based instruments come with notable advantages and have the potential to achieve a broad and uniform exposure. Aims. In this paper, we describe the first observations of meteor events with Mini-EUSO, a very wide field-of-view telescope launched in August 2019 from the Baikonur cosmodrome and installed on board the Russian Zvezda module of the International Space Station. Mini-EUSO can map the night-time Earth in the near-UV range (290-130 nm) with a field of view equal to 44 degrees x 44 degrees and a spatial resolution of about 4.7 km at an altitude of 100 km from the ground. The detector saves triggered transient phenomena with a sampling frequency of 2.5 mu s and 320 mu s, as well as a continuous acquisition at 40.96 ms scale that is suitable for meteor observations. Methods. We designed two dedicated and complementary trigger methods, together with an analysis pipeline able to estimate the main physical parameters of the observed population of meteors, such as the duration, horizontal speed, azimuth, and absolute magnitude. To compute the absolute flux of meteors from Mini-EUSO observations, we implemented a simulation framework able to estimate the detection efficiency as a function of the meteor magnitude and the background illumination conditions. Results. The instrument detected 24 thousand meteors within the first 40 data-taking sessions from November 2019 to August 2021, for a total observation time of approximately 6 days with a limiting absolute magnitude of +6. Our estimation of the absolute flux density of meteoroids in the range of mass between 10(-5) kg to 10(-1) kg was found to be comparable to other results available in the literature. Conclusions. The results of this work prove the potential for space-based observations to increase the statistics of meteor observations achievable with instruments operating on the ground. The slope of the mass distribution of meteoroids sampled with Mini-EUSO suggests a mass index of either s = 2.09 +/- 0.02 or s = 2.31 +/- 0.03, according to two different methodologies for the computation of the pre-atmospheric mass starting from the luminosity of each event.

More than three dozen submillisecond events of ELVES type (“elves”), which are the result of the interaction of the front of an electromagnetic pulse from a lightning discharge and the lower layer of the ionosphere, have been identified in the data of a UV Atmosphere orbital multichannel detector (Mini-EUSO). Each event has a characteristic annular glow pattern and occupies a significant part of the detector’s field of view, and the signal in a separate channel has an asymmetric profile with a pronounced peak. The distribution of peak times contains information about both the localization of the discharge and the altitude of the glow. In this paper, we propose a Bayesian (probabilistic) model for reconstructing ELVES events, implemented using probabilistic programming methods in PyMC-5. The capabilities of the model for determining the position of the discharge are shown using the example of several events. Methods for modifying the model to restore the discharge orientation and refine the glow height are outlined.

The complexity of modern cosmic ray observatories and the rich data sets they capture often require a sophisticated software framework to support the simulation of physical processes, detector response, as well as reconstruction and analysis of real and simulated data. Here we present the EUSO-(Off) over bar(line) under bar framework. The code base was originally developed by the Pierre Auger Collaboration, and portions of it have been adopted by other collaborations to suit their needs. We have extended this software to fulfill the requirements of Ultra-High Energy Cosmic Ray detectors and very high energy neutrino detectors developed for the Joint Exploratory Missions for an Extreme Universe Observatory (JEM-EUSO). These path-finder instruments constitute a program to chart the path to a future space-based mission like POEMMA. For completeness, we describe the overall structure of the framework developed by the Auger collaboration and continue with a description of the JEM-EUSO simulation and reconstruction capabilities. The framework is written predominantly in modern C++ (compliled against C++17) and incorporates third-party libraries chosen based on functionality and our best judgment regarding support and longevity. Modularity is a central notion in the framework design, a requirement for large collaborations in which many individuals contribute to a common code base and often want to compare different approaches to a given problem. For the same reason, the framework is designed to be highly configurable, which allows us to contend with a variety of JEM-EUSO missions and observation scenarios. We also discuss how we incorporate broad, industry-standard testing coverage which is necessary to ensure quality and maintainability of a relatively large code base, and the tools we employ to support a multitude of computing platforms and enable fast, reliable installation of external packages. Finally, we provide a few examples of simulation and reconstruction applications using EUSO-(Off) over bar(line) under bar.

The Extreme Universe Space Observatory on a Super Pressure Balloon 1 (EUSO-SPB1) was launched in 2017 April from Wanaka, New Zealand. The plan of this mission of opportunity on a NASA super pressure balloon test flight was to circle the southern hemisphere. The primary scientific goal was to make the first observations of ultra-high-energy cosmic-ray extensive air showers (EASs) by looking down on the atmosphere with an ultraviolet (UV) fluorescence telescope from suborbital altitude (33~km). After 12~days and 4~hours aloft, the flight was terminated prematurely in the Pacific Ocean. Before the flight, the instrument was tested extensively in the West Desert of Utah, USA, with UV point sources and lasers. The test results indicated that the instrument had sensitivity to EASs of approximately 3 EeV. Simulations of the telescope system, telescope on time, and realized flight trajectory predicted an observation of about 1 event assuming clear sky conditions. The effects of high clouds were estimated to reduce this value by approximately a factor of 2. A manual search and a machine-learning-based search did not find any EAS signals in these data. Here we review the EUSO-SPB1 instrument and flight and the EAS search.

EUSO-TA is a ground-based fluorescence telescope built to validate the design of ultra-high energy cosmic ray fluorescence detectors to be operated in space with the technology developed within the Joint Exploratory Missions for Extreme Universe Space Observatory (JEM-EUSO) program. It operates at the Telescope Array (TA) site in Utah, USA. With an external trigger provided by the Black Rock Mesa fluorescence detectors of the Telescope Array experiment, with EUSO-TA we observed air-showers from ultra-high energy cosmic rays, as well as laser events from the Central Laser Facility at the TA site and from portable lasers like the JEM-EUSO Global Light System prototype. Since the Black Rock Mesa fluorescence detectors have a ∼30 times larger field of view than EUSO-TA, they allow a primary energy reconstruction based on the observation of a large part of the shower evolution, including the shower maximum, while EUSO-TA observes only a part of it, usually far away from the maximum. To estimate the detection limits of EUSO-TA in energy and distance, a method was developed to re-scale their energy, taking into account that EUSO-TA observes only a portion of the air-showers. The method was applied on simulation sets with showers with different primaries, energy, direction, and impact point on the ground, as well as taking into account the experimental environment. EUSO-TA was simulated with an internal trigger and different elevation angles and electronics. The same method was then applied also to real measurements and compared to the simulations. In addition, the method can also be used to estimate the detection limits for experiments that are operated at high altitudes and in most cases can see the maximum of the showers. This was done for EUSO-SPB1, an instrument installed on a super-pressure balloon. Finally, the expected detection rates for EUSO-TA were also assessed using the prepared simulated event sets. The rates correspond to a few detections per recording session of 30 h of observation, depending on the background level and the configuration of the detector.

The present white paper is submitted as part of the "Snowmass" process to help inform the long-term plans of the United States Department of Energy and the National Science Foundation for high-energy physics. It summarizes the science questions driving the Ultra-High-Energy Cosmic-Ray (UHECR) community and provides recommendations on the strategy to answer them in the next two decades.

KLYPVE (K-EUSO) is a planned space experiment aimed at studying ultra-high-energy cosmic rays by detecting fluorescent and Cherenkov radiation from extensive air showers in the Earth’s night atmosphere from near-Earth orbit. The observatory is being developed as a part of the JEM-EUSO program. The threshold of registration will be around 50 EeV, and the annual statistics of events will be more than 50. The KLYPVE mission can significantly supplement the data of ground-based experiments.

In 2016–2017, TUS, the world’s first experiment for testing the possibility of registering ultra-high energy cosmic rays (UHECRs) by their fluorescent radiation in the night atmosphere of Earth was carried out. Since 2019, the Russian-Italian fluorescence telescope (FT) Mini-EUSO (“UV Atmosphere”) has been operating on the ISS. The stratospheric experiment EUSO-SPB2, which will employ an FT for registering UHECRs, is planned for 2023. We show how simple convolutional neural networks can be effectively used to find track-like events in the variety of data obtained with such instruments.

This is a collection of papers presented by the JEM-EUSO Collaboration at the 38th International Cosmic Ray Conference (Nagoya, Japan, July 26-August 3, 2023)

Complementing the overview contribution about the whitepaper on ultra-high-energy cosmic rays (UHECR) prepared for the Snowmass community survey in the U.S. [Astroparticle Physics 149 (2023) 102819 - arXiv:2205.05845], this contribution focuses on Chapter 6, the ‘Instrumentation Roadmap’ for UHECR physics in the next decades. In addition to an increase in statistics, a higher measurement accuracy of cosmic-ray air showers is needed to answer open questions regarding the astrophysics and particle physics related to UHECR. The needed boost in exposure can be provided by space-borne fluorescence detectors with POEMMA or by huge ground arrays using a single cost-effective technique, such as the giant radio arrays envisioned with GRAND. These observatories maximizing the exposure need to be complemented by ground arrays featuring an event-by-event resolution of the rigidity of the primary particle, which is the essence of GCOS. The required high mass resolution demands the simultaneous measurement of the electromagnetic (energy and $X_\mathrm{max}$) and muonic shower components, possibly by combining layered water-Cherenkov with radio detectors and next-generation fluorescence telescopes, together with novel analysis techniques, such as neural networks. The higher accuracy for air-shower measurements is also important for UHECR particle physics because it will enable stricter tests of hadronic interaction models and will help to identify ultra-high-energy photons or neutrinos. This contribution will give an overview of the instrumentation needed for the future of UHECR physics in the context of the next generation experiments discussed in the whitepaper.

JEM-EUSO is an international program for the development of space-based Ultra-High Energy Cosmic Ray observatories. The program consists of a series of missions which are either under development or in the data analysis phase. All instruments are based on a wide-field-of-view telescope, which operates in the near-UV range, designed to detect the fluorescence light emitted by extensive air showers in the atmosphere. We describe the simulation software ESAF in the framework of the JEM-EUSO program and explain the physical assumptions used. We present here the implementation of the JEM-EUSO, POEMMA, K-EUSO, TUS, Mini-EUSO, EUSO-SPB1 and EUSO-TA configurations in ESAF. For the first time ESAF simulation outputs are compared with experimental data.

The present white paper is submitted as part of the "Snowmass" process to help inform the long-term plans of the United States Department of Energy and the National Science Foundation for high-energy physics. It summarizes the science questions driving the Ultra-High-Energy Cosmic-Ray (UHECR) community and provides recommendations on the strategy to answer them in the next two decades.

As part of the US "Snowmass" community planning exercise, the UHECR community has come together to write a comprehensive white paper discussing the recent progress and open questions of the field, as they relate to the overarching goals of particle and astroparticle physics. The document outlines strategies and recommendations for answering these questions over the next two decades. It also proposes an integrated timeline, which considers the progress expected to be achieved by the upgraded Pierre Auger Observatory and Telescope Array experiment in this decade, and the need for a set of complementary next-generation experiments combining high-accuracy measurements (GCOS, IceCube-Gen2 with its surface array) and very high exposure at the highest energies (GRAND, POEMMA) in the next decade. The resulting document, entitled "Ultra-High Energy Cosmic-Rays: at the Intersection of the Cosmic and Energy Frontiers", appears as a special issue of Astroparticle Physics (Astropart.Phys. 149 (2023) 102819 – arXiv:2205.05845). This contribution provides a summary of the document with a focus on (selected) recommendations and proposed roadmap.

Since 2019, the Russian–Italian experiment “UV Atmosphere” (Mini-EUSO) has been operational on the International Space Station. The primary instrument of this experiment is a wide-angle telescope positioned toward nadir. Its main objective is to generate an ultraviolet map of the Earth’s nocturnal atmosphere radiation. This map serves as a crucial element in the preparation of a large-scale experiment involving the study of extremely high-energy cosmic rays using an orbiting telescope. Similar to the preceding TUS experiment, the “UV Atmosphere” instrument detects signals from various atmospheric processes in the ultraviolet range, including the luminosity of meteors. In this paper, we describe two simple neural networks that effectively extract meteor signals from the overall data stream. The proposed approach can also be applied to identify track-like signals of various origins in the data obtained from fluorescent and Cherenkov telescopes.

The Trigger Logic (TL) of the Tracking Ultraviolet Setup (TUS) and Multiwavelength Imaging New Instrument for the Extreme Universe Space Observatory (Mini-EUSO) space-based projects of the Joint Experiment Missions-EUSO (JEM-EUSO) program is summarized. The performance results on the search for Ultra-High Energy Cosmic Rays (UHECRs) are presented.

EUSO-Balloon is a pathfinder for JEM-EUSO, the mission concept of a spaceborne observatory which is designed to observe Ultra-High Energy Cosmic Ray (UHECR)-induced Extensive Air Showers (EAS) by detecting their UltraViolet (UV) light tracks “from above.” On August 25, 2014, EUSO-Balloon was launched from Timmins Stratospheric Balloon Base (Ontario, Canada) by the balloon division of the French Space Agency CNES. After reaching a floating altitude of 38 km, EUSO-Balloon imaged the UV light in the wavelength range ∼290–500 nm for more than 5 hours using the key technologies of JEM-EUSO. The flight allowed a good understanding of the performance of the detector to be developed, giving insights into possible improvements to be applied to future missions. A detailed measurement of the photoelectron counts in different atmospheric and ground conditions was achieved. By means of the simulation of the instrument response and by assuming atmospheric models, the absolute intensity of diffuse light was estimated. The instrument detected hundreds of laser tracks with similar characteristics to EASs shot by a helicopter flying underneath. These are the first recorded laser tracks measured from a fluorescence detector looking down on the atmosphere. The reconstruction of the direction of the laser tracks was performed. In this work, a review of the main results obtained by EUSO-Balloon is presented as well as implications for future space-based observations of UHECRs.

Compilation of papers presented by the JEM-EUSO Collaboration at the 37th International Cosmic Ray Conference (ICRC), held on July 12-23, 2021 (online) in Berlin, Germany.